1. Field of the Invention
This invention relates generally to a fluid control valve and, more particularly, to a proportional variable bleed solenoid valve that includes a working air gap adjustment feature to provide magnetic calibration.
2. Discussion of the Related Art
Most vehicles generally incorporate a large number of electronically controlled systems, such as an automatic transmission controller. Automatic transmission controllers typically include several solenoid operated fluid control valves that independently act to control fluid pressure in the vehicle's transmission to operate various components of the transmission. For example, solenoid operated fluid control valves are known that use transmission fluid pressure to engage and disengage the transmission clutch. One particular known solenoid valve used for this purpose is referred to as a proportional bleed solenoid valve. The proportional bleed solenoid valve provides a particular control pressure that is directly proportional to the current applied to the solenoid coil in the valve. In other words, the output control pressure is nearly linear to the current applied to the solenoid coil. These types of solenoid valves are referred to as bleed valves because they use a relatively low flow of fluid through the hydraulic portion of the valve. Solenoid operated fluid control valves are also used in other vehicle controllers besides transmission controllers.
As the controllers become more sophisticated, it is necessary that the solenoid operated fluid control valves also include advancements and improvements over the state of the art. In this regard, it becomes important to increase the operating efficiency, reduce the cost, reduce the weight, reduce the complexity, etc. of the existing solenoid operated fluid control valves. Therefore, advancements in size, part reduction, component simplification, etc. of the control valves is advantageous.
One area of improvement for proportional valves is providing a consistent control pressure. Because the component tolerances in the control valves may vary from valve to valve, the control pressure may also vary from valve to valve at the same coil current. This may be important for modern automatic transmission controllers that need to provide a consistent control pressure for a particular operation. Therefore, it is important to provide some kind of calibration of the valve at the manufacturing level of the valve so that the valve control is consistent. One area where the control pressure of a proportional solenoid valve can be calibrated is the magnetic force adjustment, where an armature position driven by the coil of the solenoid can be calibrated.
U.S. Pat. No. 5,218,999 issued Jun. 15, 1993 to Tanimoto discloses a solenoid valve that provides a mechanical adjustment of the air gap between an armature and a pole piece so the gap is consistent from valve to valve to provide a constant performance. To provide the mechanical adjustment, an elastic wave washer is interposed between the pole piece and the casing of the valve. When a lid member is fixedly attached to the casing, the wave washer is compressed to a degree depending on the dimensions of the pole piece, the coil bobbin, and a magnetic holder to set the air gap at a constant dimension.
Although the solenoid valve described in the '999 patent offers one technique for adjusting the air gap between the armature and the pole piece to provide magnetic calibration, this technique is also susceptible to the tolerances of the elastic washer, as well as including other disadvantages. Therefore, there is still room for improvement in solenoid valves to provide a magnetic force adjustment for magnetic calibration.